Transcoding

Transcoding on the IMG 2020 is the conversion from either one Codec to a different Codec as well as from one Payload Size within the Codec to a different Payload Size within the same Codec. The IMG 2020 supports integrated transcoding while using the SIP, the H.323, and Video Codecs. For IMG use cases of the IMG 2020 where transcoding of media is required, a Transcoding license must be available for each leg or channel of the call. Below is a diagram displaying a few typical transcoding scenarios where the IMG 2020 trans-codes the RTP or video as they are passed through.

As displayed in the diagram above, the IMG 2020 can transcode audio legs between the SIP protocol and the H.323 protocol; no video transcoding is supported for H.323. All codecs are supported in the SIP protocol but not all codecs are supported in the H.323 protocol. Refer to the tables below for codec support information. If the codec is supported, then it can be transcoded between the incoming and outgoing channel groups.

CODEC	SIP (Audio)	H.323 (Audio)
G.711 alaw/ulaw	Yes	Yes
G.722	Yes	Not Supported
G.723 5.3 Kbps	Yes	Yes
G.723 5.3 Kbps	Yes	Yes
G.729A/B	Yes	Yes
T.38	Yes	Yes
iLBC 20 ms	Yes	Not Supported
iLBC 30 ms	Yes	Not Supported
AMR-NB	Yes	Not Supported
AMR-WB	Yes	Not Supported
G.726-32/G.721 Static Payload	Yes	Not Supported
G.726-32/G.721 Dynamic Payload	Yes	Not Supported
GSM-FR Static Payload	Yes	Not Supported
GSM-FR Dynamic Payload	Yes	Not Supported
GSM-EFR	Yes	Not Supported
Clear Channel Codec	Yes	Not Supported

Codec	SIP (Video)
MPEG-4	Yes
H.264	Yes
H.263-2000	Yes

The two tables above are also displayed in the topic.

Codecs/Maximum IP Transcoding Sessions

A Transcoding session uses two IP ports. One port for incoming and second port for outgoing. The IMG 2020 utilized as a Session Border Controller supports a maximum of 2250 transcoding sessions (4500 ports/2= 2250 Sessions) unless the AMR codec is being used as part of the transcoding leg. If AMR codec is being used, the number of transcoding sessions will be reduced.

Codecs/Licensing

For information on what is required for licensing, refer to the Licensing (Gateway Mode) depending on your application.

Configuration

Configuration dictates that an IP Profile be created with the required codecs that will be transcoded. Below is screen capture of an IP Profile with the Vocoder Profiles configured under it.

Create Vocoder Profile with Codec that will be transcoded under it.

The IP Profile configured above is then linked to the incoming and outgoing channel groups as required.

The transcoding license must be loaded and available.

For a procedure explaining how to create an IP to IP configuration refer to the SIP to SIP - Configuration Example section. This section has four separate topics that describe a step by step procedure on how to achieve a SIP to SIP configuration.

Media / IP Transcoding Supported

The tables below display the transcoding ability of the IMG 2020 when utilizing the SIP protocol to transcode Audio Calls.

SIP to SIP

SIP to SIP	G.711(mu & a-law)	G.722	G.723.1(5.3 & 6.3 kbps)	G.726-32 / G.721	G.729 A/B	AMR-NB	AMR-WB	iLBC	Clear Channel	GSM-FR	GSM-EFR
G.711		x	x	x	x	x	x	x	x	x	x
G.722	x		x	x	x	x	x	x	x	x	x
G.723.1	x	x		x	x	x	x	x	x	x	x
G.726-32/G.721	x	x	x		x	x	x	x	x	x	x
G.729 A/B	x	x	x	x		x	x	x	x	x	x
AMR-NB	x	x	x	x	x		x	x	x	x	x
AMR-WB	x	x	x	x	x	x		x	x	x	x
iLBC	x	x	x	x	x	x	x		x	x	x
Clear Channel	x	x	x	x	x	x	x	x		x	x
GSM-FR	x	x	x	x	x	x	x	x	x		x
GSM-EFR	x	x	x	x	x	x	x	x	x	x

H.323 to H.323

H.323 to H.323	G.711(mu & a-law)	G.723.1(5.3 & 6.3 kbps)	G.729 A/B
G.711		x	x
G.723.1	x		x
G.729 A/B	x	x

SIP to H.323

SIP to H.323	G.711(mu & a-law)	G.723.1(5.3 & 6.3 kbps)	G.729 A/B
G.711		x	x
G.723.1	x		x
G.729 A/B	x	x